1. Field Of The Invention
This invention relates to a scroll type compressor, and more particularly, to an axial sealing mechanism for the scroll members of a scroll type compressor.
2. Description Of The Prior Art
A conventional scroll type compressor with an axial sealing mechanism for axially sealing the scroll members is illustrated in FIG. 1. The axial sealing mechanism shown in FIG. 1 is similar to the axial sealing mechanism described in U.S. Pat. No. 4,475,874. The scroll type compressor includes fixed scroll 10 having circular end plate 11 from which spiral element 12 extends, and orbiting scroll 20 having circular end plate 21 from which spiral element 22 extends. Block member 30 is attached to circular end plate 11 by a plurality of fastening members, such as bolts 15, to define chamber 40 in which orbiting scroll 20 is disposed. Spiral elements 12 and 22 are interfitted at an angular and radial offset to make a plurality of line contacts to define at least one pair of sealed-off fluid pockets. Driving mechanism 50 includes drive shaft 51 rotatably supported in bore 31 which is centrally formed in block member 30. Bushing 53 is integrally formed at one end of drive shaft 51. Immediately below bushing 53 is bearing 511 which is disposed between an outer peripheral surface of drive shaft 51 and an inner peripheral surface of bore 31. Projecting from a surface of circular end plate 21 opposite spiral element 22 of orbiting scroll 20 is circular boss 23. Circular boss 23 is rotatably inserted into circular depression 531 of bushing 53 through bearing 231. The center of circular boss 23 is radially offset from the center of drive shaft 51, such that orbiting scroll 20 will orbit when drive shaft 51 rotates.
Circular end plate 21 of orbiting scroll 20 divides chamber 40 into first chamber 41 in which spiral elements 12 and 22 are disposed and second chamber 42 in which Oldham coupling 60 and bushing 53 of driving mechanism 50 are disposed. A mechanical seal (not shown) is mounted in block member 30 below bearing 511 and adjacent drive shaft 51. The mechanical seal is used for preventing fluid communication between second chamber 42 and the atmosphere or another chamber surrounding the compressor.
Discharge port 70 is formed at a central portion of circular end plate 11 to discharge the compressed fluid from a central fluid pocket. Suction port 80 is formed at a peripheral portion of circular end plate 11 to supply suction fluid to the outermost fluid pockets. A pair of apertures 90 which are sized to produce a pressure throttling effect are formed at a middle portion of circular end plate 21 of orbiting scroll 20 to link second chamber 42 to a pair of intermediately compressed fluid pockets 41a.
During operation of the compressor, the pressure in intermediate fluid pockets 41a fluctuates within a defined range. Thus, even at a steady-state operating condition of the compressor, the pressure in second chamber 42, is at best a varying average pressure of the range of pressures in intermediate fluid pockets 41a. Accordingly, the axial sealing force applied against orbiting scroll 20 to urge it into sealing engagement with fixed scroll 10 is a function of the average intermediate pressure in second chamber 42.
One of the disadvantages of the above prior art axial sealing mechanism is that, since second chamber 42 admits the intermediately compressed fluid from intermediate fluid pocket 41a in which pressure fluctuates within a range of pressures, the pressure in second chamber 42 also fluctuates thereby varying the axial sealing force applied to the orbiting scroll. This occurs even in the steady-state operating condition of the compressor. As a result, Oldham coupling 60 and driving mechanism 50 intermittently receive an undesirable thrust force which is generated by the reaction force of the compressed fluid in all the fluid pockets. These thrust forces reduce the durability and life of the compressor.
Another disadvantage of the above prior art axial sealing mechanism is that the machining process for forming aperture 90 in circular end plate 21 must be very precise. The more precise the machining the greater the increase in manufacturing costs. If precise tolerances are not achieved it may lead to reduced operating efficiency.
Another disadvantage of the above prior art is that an axial sealing mechanism must be provided which increases the manufacturing costs.